U.S. patent number 4,513,023 [Application Number 06/468,936] was granted by the patent office on 1985-04-23 for method of constructing thin electroluminescent lamp assemblies.
This patent grant is currently assigned to Union Carbide Corporation. Invention is credited to John Wary.
United States Patent |
4,513,023 |
Wary |
April 23, 1985 |
Method of constructing thin electroluminescent lamp assemblies
Abstract
A method of constructing a thin electroluminescent lamp assembly
comprising forming a UV curable dielectric matrix by loading
nonencapsulated particles of electroluminescent phosphor into a UV
curable dielectric composition, depositing a coating of such
composition over the surface of a transparent conductor, curing
such composition by exposure to ultraviolet light in a
substantially inert atmosphere, interposing a coating of a silver
conductive material in the form of a band about the periphery of
the transparent conductor to form an electrical bus bar with the
band having an elongated section of the same composition extending
therefrom to form a first electrical lead, curing said band and
electrical lead, superimposing a conductive coating over the
surface of the UV curable dielectric composition with the
conductive coating having an elongated section extending therefrom
to form a second electrical lead laterally spaced apart from the
first electrical lead, curing the conductive coating and second
electrical lead and applying a protective coatings over said
conductive coatings.
Inventors: |
Wary; John (Noblesville,
IN) |
Assignee: |
Union Carbide Corporation
(Danbury, CT)
|
Family
ID: |
23861822 |
Appl.
No.: |
06/468,936 |
Filed: |
February 23, 1983 |
Current U.S.
Class: |
427/511; 313/503;
427/517; 427/66 |
Current CPC
Class: |
H05B
33/10 (20130101) |
Current International
Class: |
H05B
33/10 (20060101); B05D 003/06 () |
Field of
Search: |
;427/54.1,44,53.1,66
;430/139 ;313/498,503,505 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Newsome; John H.
Attorney, Agent or Firm: Lieberstein; E.
Claims
I claim:
1. A method of constructing a thin electroluminescent lamp
comprising the steps of:
(a) screen printing a band of silver conductive material
substantially around the edges of a circumscribed area of a
transparent conductive substrate with said area conforming to the
desired configuration for the lamp and with said band forming an
electrical bus bar for the lamp;
(b) forming an insulated support area over a section of said
transparent conductive substrate extending from said silver
conductive bus bar;
(c) depositing a finger-like section of silver conductive material
over said insulated support area and extending from said bus bar to
form a first electrical lead;
(d) forming a UV curable dielectric matrix by loading
nonencapsulated particles of electroluminescent phosphor into a UV
curable dielectric composition;
(e) depositing a coating of said UV curable dielectric composition
over said circumscribed area of the transparent conductor and over
said silver conductive bus bar;
(f) curing said coating composition by exposure to a source of
ultraviolet light in a substantially inert atmosphere;
(g) superimposing a layer of a nontransparent conductive material
over the surface of the UV curable dielectric coating with said
nontransparent conductive layer having an elongated finger-like
section extending over said insulating support area to form a
second electrical lead laterally spaced from said first electrical
lead; and
(h) applying a protective coating over said conductive layer and at
least a portion of said first and second electrical leads.
2. A method as defined in claim 1 wherein said transparent
conductor is formed by depositing a thin layer of conductive
particles selected from the group consisting of gold, indium tin
oxide and indium oxide over the surface of a transparent sheet of a
resinous material.
3. A method as defined in claim 2 wherein said phosphor particles
in said UV curable dielectric matrix comprises at least about 50%
by weight of the total composition.
4. A method as defined in claim 3 wherein said nontransparent
conductive layer is formed by coating the surface of said UV
curable dielectric coating with a conductive composition and curing
said conductive composition.
5. A method as defined in claim 3 wherein said nontransparent
conductive layer is formed by bonding a layer of conductive sheet
material to said UV curable dielectric coating.
6. A method of constructing a thin electroluminescent lamp
comprising the steps of:
(a) depositing a layer of a transparent conductive material, upon
an insulating substrate to form a predetermined shape substantially
conforming to the desired configuration for the lamp, with the
transparent conductor having an elongated finger-like section
forming a first electrical lead for the lamp;
(b) screen printing a band of silver conductive material
substantially around the edges of the predetermined shape formed by
said transparent conductor for forming an electrical bus bar for
the lamp;
(c) forming a UV curable dielectric matrix by loading
nonencapsulated particles of electroluminescent phosphor into a UV
curable dielectric composition;
(d) depositing a coating of said UV curable dielectric composition
over the transparent conductor and over said silver conductive bus
bar with said first electrical lead exposed;
(e) curing said coating composition by exposure to a source of
ultraviolet light in a substantially inert atmosphere;
(f) superimposing a layer of a nontransparent conductive material
over the surface of the UV curable dielectric coating with said
nontransparent conductive layer having an elongated finger-like
section extending over said insulating substrate in registry with
and laterally spaced from said first electrical lead to form a
second electrical lead;
(g) applying a protective coating over said nontransparent
conductive layer and extending over at least a portion of said
first and second electrical leads.
7. A method as defined in claim 6 wherein said transparent
conductor is formed by depositing a thin layer of conductive
particles selected from the group consisting of gold, indium tin
oxide and indium oxide over the surface of a transparent sheet of a
resinous material.
8. A method as defined in claim 7 wherein said phosphor particles
in said UV curable dielectric matrix comprises at least about 50%
by weight of the total composition.
9. A method as defined in claim 8 wherein said nontransparent
conductive layer is formed by coating the surface of said UV
curable dielectric coating with a conductive composition and curing
said conductive composition.
10. A method as defined in claim 9 wherein said nontransparent
conductive layer is formed by bonding a layer of conductive sheet
material to said UV curable dielectric coating.
11. A method of constructing a thin electroluminescent lamp
comprising the steps of:
(a) forming a UV curable dielectric matrix by loading
nonencapsulated particles of electroluminescent phosphor into a UV
curable dielectric composition;
(b) depositing a coating of such composition upon a predetermined
surface area of a nontransparent conductor, said area conforming to
the desired configuration for the lamp and with said nontransparent
conductor having a predetermined finger-like section forming a
first electrical lead for the lamp;
(c) curing said coating composition by exposure to a source of
ultraviolet light in a substantially inert atmosphere;
(d) forming an insulated support area over a section of said
nontransparent conductor adjacent to said predetermined surface
area and said first electrical lead;
(e) screen printing a band of silver conductive material
substantially around the periphery of said coating of dielectric
matrix composition for forming a bus bar for the lamp;
(f) screen printing a finger-like extension of said silver
conductive material from said bus bar over said insulated support
area to form a second electrical lead adjacent to said first
electrical lead;
(g) superimposing a coating of a transparent conductive material
over said coating of dielectric matrix material and over said bus
bar; and
(h) applying a protective coating over said transparent conductive
coating and extending over at least a portion of said first and
second electrical leads.
12. A method as defined in claim 11 wherein said transparent
conductor is formed by depositing a thin layer of conductive
particles selected from the group consisting of gold, indium tin
oxide and indium oxide over the surface of a transparent sheet of a
resinous material.
13. A method as defined in claim 12 wherein said phosphor particles
in said UV curable dielectric matrix comprises at least about 50%
by weight of the total composition.
14. A method as defined in claim 13 wherein said nontransparent
conductive layer is formed by coating the surface of said UV
curable dielectric coating with a conductive composition and curing
said conductive composition.
15. A method as defined in claim 14 wherein said nontransparent
conductive layer is formed by bonding a layer of conductive sheet
material to said UV curable dielectric coating.
16. A method of constructing a thin electroluminescent lamp
comprising the steps of:
(a) depositing a layer of nontransparent conductive material,
having a predetermined shape substantially conforming to the
desired configuration for the lamp, upon an insulating substrate,
with the nontransparent conductor having an elongated finger-like
section for forming a first electrical lead for the lamp;
(b) forming a UV curable dielectric matrix by loading
nonencapsulated particles of electroluminescent phosphor into a UV
curable dielectric composition;
(c) depositing a coating of such matrix material composition over
said layer of nontransparent conductive material with said first
electrical lead exposed;
(d) curing said coating by exposure to ultraviolet light in a
substantially inert atmosphere;
(e) screen printing a band of silver conductive material
substantially around the periphery of said dielectric matrix
coating for forming a bus bar for the lamp;
(f) screen printing a finger-like extension of said silver
conductive material from said bus bar over said insulating
substrate to form a second electrical lead adjacent to said first
electrical lead;
(g) superimposing a coating of a transparent conductive material
over said coating of dielectric matrix material and over said bus
bar; and
(h) applying a protective coating over said transparent conductive
coating and extending over at least a portion of said first and
second electrical leads.
17. A method as defined in claim 5 wherein said phosphor particles
in said UV curable dielectric matrix comprises at least about 50%
by weight of the total composition.
18. A method as defined in claim 17 wherein said nontransparent
conductive layer is formed by coating with a conductive composition
and curing said conductive composition.
19. A method as defined in claim 19 wherein said nontransparent
conductive layer is formed by bonding a layer of conductive sheet
material to said UV curable dielectric coating.
Description
This invention relates to a method of manufacturing visible display
devices from electroluminescent phosphors and more particularly to
a method of making an electroluminescent light source such as a
lamp in the form of a thin, flexible multi-layered assembly.
An electroluminescent lamp is basically composed of a layer of
electroluminescent phosphor material typically of a metal activated
zinc sulphide placed between two conductive layers one of which is
transparent. When an alternating electric field is impressed across
the conductors the phosphors are excited and emit photons with
almost all of the radiated energy lying within the visible light
spectrum. The emission spectrum and wavelength generated by the
phosphors is controlled by the activator element such as copper or
manganese.
Electroluminescent phosphors are inherently hygroscopic and
sensitive to heat and moisture. When exposed to an excess of heat
or high humidity the phosphor particles are damaged. The
sensitivity of the phosphor particles to moisture is so strong that
exposure even to conditions of low humidity will affect efficiency
and decrease the light output capacity of the lamp in which the
phosphors are incoporated. To reduce the susceptibility of the
electroluminescent phosphors to heat, and more specifically to
moisture, it has become the customary practice to microencapsulate
the electroluminescent phosphor particles in protective enclosures
composed of organic sealants. The microencapsulated particles are
then incorporated in a conventional solvent based high dielectric
medium typically comprising a cyanoethylcellulose solution or
another suitable organic polymeric matrix dissolved in a solvent
for forming an intermediate layer in the fabrication of a laminated
electroluminescent lamp assembly.
An electroluminescent lamp is currently fabricated starting with a
conductive non-transparent substrate of, for example, a sheet of
aluminum foil upon which is coated an insulating layer of high
dielectric constant material such as barium titinate. An embedment
of microencapsulated electroluminescent phosphor in an appropriate
solvent based composition is deposited over the dielectric layer. A
transparent conductive coating formed from, for example, indium
oxide and/or tin indium oxide is then deposited over the phosphor
layer. A bus bar having a conductivity greater than the
conductivity of the transparent conductor is applied around the
periphery of the transparent conductor with electrical leads joined
to both the bus bar and the aluminum foil conductor. The entire
assembly excluding the connecting leads is then laminated together
using plastic sheets of polyester or polycarbonate. The composition
of each intermediate layer, viz., the barium titanate layer, the
layer of electroluminescent phosphor composition, the indium oxide
and/or tin indium oxide layer and the bus bar conductor are all
solvent based coatings which are deposited in succession. A typical
solvent based system may include toluene, acetone,
dimethylformamide and/or tetrahydrofuran or other conventional
solvents. Each solvent based layer in succession is exposed to heat
to drive off the solvent before application of a subsequent layer.
This manufacturing procedure is labor intensive and time consuming
and has an inherent quality control problem resulting in a
considerable number of unusable lamps. The high failure rate is
believed to be the result of the successive application of solvent
based layers. Each successive layer tends to resolvate the
underlying layers thereby creating bleed-through pin-holes in the
interlayered structure, which act as sites for electrical break
down and failure of the structure. Another contributing factor to
the high failure rate in the current manufacture of
electroluminescent lamps may be due to ingress of moisture and/or
contaminants through the electrical lead connection to the
conducting layers. Presently, the electical leads are physically
joined to the bus bar and solid conductor before the lamp is
laminated. The electrical connections are difficult to seal off
from the atmosphere.
An electroluminescent lamp fabricated in accordance with the method
of the present invention possesses the characteristic of
substantially increased resistance to moisture while allowing for
substantially reduced costs of production. Increased moisture
resistance is achieved in accordance with the present invention by
incorporating the electroluminescent phosphor material in a UV
curable matrix and exposing the matrix to ultraviolet "UV" light in
a substantially inert atmosphere. It has further been found that
the current manufacturing practice of microencapsulating the
phosphors can be eliminated provided the phosphors are loaded into
a dielectric matrix which is UV cured in a substantially inert
atmosphere preferably of nitrogen. In addition since the phosphor
loaded dielectric matrix is disposed intermediate the conductive
layers only the phosphor loaded matrix layer need be cured by
exposure to "UV" although from a cost standpoint UV curing of each
layer is desirable. The method of the present invention also
eliminates the prior art problem associated with joined electrical
leads.
Accordingly, it is the principle object of the present invention to
provide a method of constructing a thin flexible multi-layered
electroluminescent lamp assembly having a substantially decreased
susceptibility to humidity.
It is a further object of the present invention to provide a method
of constructing an electroluminescent lamp which eliminates the
conventional requirement for microencapsulation of the
electroluminescent phosphors and the necessity for interposing an
independent layer of barium titanate between the phosphor layer and
the conductive layers.
Other objects and advantages of the present invention will become
apparent from the following detailed explanation of the invention
when read in conjunction with the following drawings in which:
FIG. 1 is an exploded view in perspective of the multi-layered
electroluminescent lamp assembly of the present invention;
FIG. 2 is an exploded view in perspective of an alternative
arrangement for the multi-layered lamp assembly of FIG. 1; and
FIG. 3 is a perspective view of the fully assembled lamp of FIG.
1.
FIGS. 1 and 2 illustrate the method of the present invention for
constructing a multi-layered electroluminescent lamp assembly. The
fully assembled lamp is shown in FIG. 3. The lamp 10 may be
constructed in accordance with the present invention starting with
a transparent conductor 12 as the substrate or, conversely,
starting from the opposite side of the lamp 10, using a
non-transparent conductor 14 as the substrate. The transparent
conductor 12 is hereafter referred to as the "light side" of the
lamp whereas the non-transparent conductor 14 is hereafter referred
to as the "dark side" of the lamp 10.
In assembling the lamp 10 from the light side up it is preferable
for the transparent conductive substrate 12 to be formed from a
sheet 16 of transparent polyester or polycarbonate having a
metalized surface 18. The metalized surface 18 may be deposited by
conventional vacuum metalizing techniques. The metalized surface 18
can be formed using materials such as; Indium oxide, Indium tin
oxide or gold with the gold sputtered surface being illustrated
herein. The thickness of the gold sputtered surface 18 is of the
order of 4 angstroms. The ultra thin layer of gold 18 renders the
underlying plastic sheet 16 conductive without substantially losing
its transparency to light. Alternately, the transparent conductive
substrate 12 may be formed by coating the sheet 16 with a thin
layer of indium tin oxide or simply indium oxide and curing the
coated layer.
An insulating pad 19 is screen printed upon the gold sputtered
surface side of the transparent conductive substrate. The
insulating composition for the pad 19 is preferably a conventional
UV curable screen printable solder resist as is commercially
available by the Dexter Corporation of Industry California under
the tradename Hysol SR7100. The pad 19 is cured by exposure to
ultraviolet light.
A conventional solvent based silver conductive composition is
screen printed over the gold sputtered surface 18 to form a band 20
having a predetermined pattern which substantially encloses the
perimeter of the transparent conductive substrate 12. The screen
printed silver band 20 functions as an electrical bus bar for the
conductive substrate 12 to uniformly distribute an applied EMF over
the gold sputtered surface 18. Preferably the bus bar 20 should
have an opening 22. An electrical lead 24 is simultaneously screen
printed as an extension of the bus bar 20. The electrical lead 24
may be printed on the transparent conductor 12 directly over the
pad 19. The end 25 of the pad 19 may lie contiguous to the side 26
of the bus bar 20 from which the electrical lead 24 extends. It
should be noted that the electrical lead 24 and bus bar 20 form a
single unitary coating thereby avoiding joining techniques. The
electrical lead 24 is adapted to be connected to one terminal of an
alternating source of voltage (not shown). A commercially available
silver conductive composition for use as a screen printable silver
conductive ink is sold by the Acheson Colloids Company of Port
Huron Michigan under the tradename Electrodag 427SS. The silver
based conductive composition forming the bus bar 20 is cured in the
presence of heat in a conventional oven. It is however within the
scope of the present invention to use a UV curable silver
conductive composition in forming the bus bar 20 which would then
be cured by exposure to a source of ultraviolet light.
The next step of the process is to deposit a coating 28 of a UV
curable dielectric matrix formed by loading non-encapsulated
electroluminescent phosphors in a conventional UV curable
dielectric composition. It is preferred that the electroluminescent
phosphors be uniformly distributed within the dielectric
composition and should represent at least about 50% by weight of
the total UV curable dielectric matrix. The phosphor particles may
be loaded into any conventional UV curable dielectric composition
such as, for example, the UV curable dielectric 5011D which is
available from the Dupont Co. Inc. of Delaware U.S.A.
The phosphor loaded dielectric matrix coating 28 is cured by
exposure to an ultraviolet source in an inert atmosphere. Any
conventional ultraviolet light source may be used including mercury
lamps, spectrally controlled mercury lamps, black lights, and
germicidal lamps. A conventional full spectrum medium pressure
mercury lamp system is disclosed in U.S. Pat. No. 3,933,385 the
teachings of which is incorporated herein by reference. The coating
is applied to the transparent substrate 12 using any conventional
deposition technique such as screen printing, air-knife coating,
roll coating, gravure coating, extension coating, bead coating,
curtain coating and so forth.
Curing by exposure to ultraviolet radiation includes any range of
wavelengths in the electromagnetic spectrum from 100 to about 4000
Angstroms. It is however critical to the present invention that the
UV curable phosphor loaded dielectric matrix coating 28 be cured in
an inert atmosphere preferably of nitrogen. Curing in an inert
atmosphere increases the stability of the dielectric matrix
containing the electroluminescent phosphors thereby decreasing the
susceptibility and sensitivity of the lamp assembly to moisture.
Moreover, by curing in an inert atmosphere substantially less heat
is present in curing the matrix which also increases the stability
and resistance of the dielectric matrix to moisture. Moreover, the
dielectric properties of the matrix may also be substantially
improved as a result of curing in an inert atmosphere due to less
residual uncured monomer. The coating thickness and phosphor
loading will determine the length of time it takes to fully cure
the dielectric matrix coating 28. The coating thickness may vary
with the amount of phosphor material in the dielectric which is in
turn related to the desired properties for the lamp. In general the
dielectric matrix coating 28 will vary from 0.2 mils to 1.2 mils
thick.
In the embodiment of FIG. 1 the coating 28 covers an area at least
embracing the area enclosed by the bus bar 20 with the electrical
lead 24 exposed. In general the configuration of the coating 28
will define the geometry of the lamp 10 since this is the area that
lights up. Although a rectangular geometry is shown in FIG. 1 it is
intended only for illustrative purposes. The lamp 10 may be
constructed of any planar geometrical configuration.
The non-transparent conductor 14 is then superimposed over the
coating 28. An electrical lead 33 extends from the non-transparent
conductor 14. The electrical lead 33 is formed as an integral part
of the non-transparent conductor 14 so as to define a single
unitary structure. The non-transparent conductor 14 and electrical
lead 33 may be formed as a unitary structure out of a sheet of
aluminum or other electrically conductive material and bonded in
place over the coating 28 such that the electrical lead 33 is
positioned over the insulating pad 19 adjacent to and separated
from the electrical lead 24. Alternately the non-transparent
conductor 14 and the electrical lead 33 may be formed as a unitary
coating by screen printing a composition of electrically conductive
material such as the silver conductive composition used in forming
the electrical bus bar 20.
The lamp 10 may then be completed for the embodiment of FIG. 1 by
superimposing a protective covering 35 over the conductor 14 which
preferably also covers the electrical leads 33 and 24 except for an
exposed area 37 which is left uncovered to enable the leads 33 and
24 to be electrically coupled to any standard electrical connector
(not shown) which in turn is connected to the opposite terminals of
an alternating source of voltage (not shown). Another protective
covering 40 may also be placed beneath the transparent conductor
12. The protective coverings 35 and 40 may represent sheets of
plastic such as polyester or polycarbonate or they may be formed
using a screen printed clear protective coating of a screen ink
formulation. Typical screen ink formulations may be found in U.S.
Pat. No. 3,808,109 and in "UC curing: Science and Technology"
edited by S. Pappes Technology Marketing Corporation 1973 both
incorporated herein by reference. The screen ink formulation may be
conventionally heat cured or UV cured. A typical UV curable screen
ink formulation includes a light sensitizing photo initiator, an
oligimer, a monomer and a crosslinking agent. Waste material
representing any excess material extending beyond the boundary of
the coating 28 may then be cut out to form a finished lamp assembly
as shown in FIG. 3.
The lamp assembly of the present invention may also be made
starting from the non-transparent conductor or "dark side" up as
shown in FIG. 2. In this instance a strip of a solid conductor,
such as aluminum foil may serve as the non-transparent conductor
60. Alternatively the non-transparent conductor 60 may be formed
using a sheet of aluminum or copper foil or a sheet of laminized or
metalized aluminum or copper on a polycarbonate, polyester or other
non-conductive substrate.
An insulating pad 62 is then screen printed over the
non-transparent conductor 60. The insulating pad 62 is composed of
a screen printable solder resist composition corresponding to the
insulating pad 19 of FIG. 1. A section 63 of the insulating pad 62
is removed or masked out during printing to expose a corresponding
section 63 of the non-transparent conductor 60. The exposed section
63 of the conductor 60 will serve as one electrical lead of the
lamp assembly.
A coating 64 of a UV curable phosphor loaded dielectric matrix
composition is then screen printed over the non-transparent
conductor 60 in a defined area representing any predetermined
geometry. The coating 64 is screen printed in registry with the
insulating pad 62 so that they substantially abut one another with
the insulating pad 62 extending from one end 66 of the coating 64.
The insulating pad 62 may alternatively be screen printed over the
conductor 60 following the printing and curing of the matrix
coating 64.
The geometry of the phosphor loaded dielectric matrix coating 64
defines the geometry of the lamp 11 and may be represented by any
geometrical configuration. The phosphor loaded dielectric matrix
coating 64 has a composition identical to the corresponding
dielectric matrix layer 28 used in the construction of the lamp
assembly 10 of FIG. 1. The phosphor loaded dielectric matrix
coating 64 is cured by exposure to a source of ultraviolet light in
a controlled inert gas atmosphere of preferably nitrogen in the
same manner as discussed heretofore with respect to the dielectric
matrix layer 28 of FIG. 1.
A band 70 of a conventional solvent based silver conductive
composition equivalent to the silver conductive band 20 of FIG. 1
is screen printed over the phosphor loaded dielectric matrix
coating 64. The band 70 should form a pattern which substantially
encloses the perimeter of the phosphor loaded dielectric matrix
coating 64. The silver conductive band 70 should have an opening 72
on one side and a pigtail 74, representing an electrical conducting
lead, extending from its opposite side over the insulating pad 62
and in registry with but laterally spaced from the section 63.
A transparent conductive coating 76 is then deposited in registry
over the band 70 and the phosphor loaded dielectric matrix coating
64. The transparent conductive layer 76 is preferably formed from
an indium-tin oxide or simply indium oxide coating in a convention
solvent based or UV based composition. In the latter case the
transparent conductive coating 76 would be cured by exposure to a
source of ultraviolet radiation. The transparent conductive layer
76 may also be formed by bonding a transparent conductive substrate
such as 12 in FIG. 1 over the band 70. The silver conductive band
70 functions as an electrical bus bar to uniformly distribute an
applied EMF over the surface of the transparent conductive coating
76. The applied EMF is provided by coupling the electrical leads
formed through the exposed section 63 and the pigtail 74 to a
source of alternating potential (not shown) using a conventional
connector (not shown).
A protective coating 78 may be applied over the surface of the
transparent conductive coating 76. The protective coating 78 should
leave a predetermined length of the electrical leads 63 and 74
exposed. Another protective coating 79 may, if desired, be applied
to the undersurface of the non-transparent conductor 60. The
protective coating(s) may be screen printed or laminated in a
manner corresponding to the formation of the protective coatings 35
and 40 to form the finished lamp assembly 11.
The insulating pad 19 in FIG. 1 and the insulating pad 62 in FIG. 2
is employed solely to isolate the electrical leads and to permit
connection to a standard connector. It should be apparent that
other printing or masking techniques or assembly arrangements may
be employed which may obviate the need for the insulating pads or
for using the pads in the precise manner discussed in connection
with the embodiments of FIGS. 1 and 2. For example in the FIG. 1
embodiment if a plastic sheet is used as a substrate the conductor
may be coated over a predetermined area defined by the area of the
dielectric matrix and thereby avoid the need for the dielectric
pad. Also in the FIG. 2 embodiment the non-transparent conductor
may be formed with an extended section representing an electrical
lead. If the non-transparent conductor is then coated on an
insulative substrate the need for the insulating pad is
avoided.
* * * * *